Monobromacetic Acid, CH2Br.COOH.
Hell, Bcr.) 1881, 14, 891 ; Volhard, Annalen, 1887, 242,
141 ; Zelinsky, Ber., 1887, 20, 2026.
30 grms. (30 c.c.) glacial acetic acid.
I05 3) (35 c.c.) bromine.
5 „ red phosphorus.
All the above substances must be dry. The acetic acid is frozen in
ice, and any liquid drained off, and the red phosphorus is washed
with water to free it from phosphoric acid, dried in the steam oven,
and kept over sulphuric acid in a desiccator until required. The
bromine is placed in a separating funnel with half its volume of
concentrated sulphuric acid overnight, and
then separated. The apparatus is shown in
Fig- 63 . It consists of a round flask (250 c.c.)
attached to an upright condenser, which is
provided with a cork. A tap-funnel con-
taining the bromine passes through one
hole, and a wide bent tube, attached at its
lower end to a funnel, passes through the other.
As a large quantity of hydrobromic acid is
evolved in the reaction, the funnel is made to
touch the surface of water contained in a
beaker, whereby it is completely absorbed.
The phosphorus and acetic acid are placed
in the flask, and bromine dropped in from the
tap-funnel.* A vigorous reaction occurs, and
the liquid becomes very warm. After half
the bromine has been added the action
moderates, and the remainder may be run in
more quickly. When the whole has been
added, the liquid is boiled gently until the colour of the
bromine disappears. It is now allowed to cool, and the
liquid decanted into a distilling flask for distillation in vacua.
Care must be taken not to touch the substance with the hands,
as even a small quantity produces very unpleasant sores. The
apparatus for distilling in vacua is shown in Fig. 56 (p. 85).